1. Field of the Invention
The present invention relates to a tapered bristle for a toothbrush, and a toothbrush with a tuft of tapered bristles. In addition, the present invention relates to methods for producing said tapered bristle or said toothbrush.
2. Description of the Prior Art
The filament generally used for toothbrush bristles is made from nylon The advantages of nylon-made filament are its proper flexibility and softness. However, the disadvantages of nylon-made filament are that it is very water-absorbent and easily deformed. Typically, nylon-made bristle ends of toothbrushes are rounded off, as shown in FIG. 1, so that damage to the gums is avoided during brushing.
Polyester compounds such as polybutylene telephthalate (hereinafter PBT) and polyethylene terephthalate (hereinafter PET) may be used as the filament for toothbrush bristles. PBT and PET are better than nylon for toothbrush bristles in that they are cheaper, more durable, and less water-absorbent. However, PBT and PET are too stiff and inflexible, and thus, not soft. As such, since it appears that toothbrush bristles me from PBT or PET damage the gums, PBT or PET usually have been used only in inexpensive disposable toothbrushes, or in combination with nylon-made bristles, as a way to reduce the cost.
A process for tapering off the ends of PBT or PET-made bristles resulting in a needle-shape was suggested as a way to eliminate the disadvantages of PBT or PET while keeping the advantages. Typically, this was done mechanically by tapering off the bristle ends with the blade of a knife or with a rounding machine. This mechanical process produces tapered bristle with ends being only rounded, as shown in FIG. 2. However, it is impossible to produce tapered bristle with ends being needle-like by the mechanical process. Therefore, the mechanical process failed to sufficiently diminish the cited disadvantages of PBT or PET.
To produce PBT or PET-made toothbrush bristles with needle-like highly tapered ends, a method for tapering off the ends of said bristles using a sulfuric acid solution was developed by the present inventor and was patented as Korean Patent No. 130932, the disclosure of which is incorporated herein by reference. This technique comprises (i) cutting PBT or PET filament so that from about 1 mm to about 4 mm is extended from the desired length of bristles, (ii) soaking one end of the cut filament vertically in from 60% to 98% sulfuric acid solution at a temperature of from 80.degree. C. to 200.degree. C. by the length of from about 8 mm to about 9 mm, followed by treating another end of the filament in the same manner, (iii) cooling the resulting appropriately tapered filament in cold water, (iv) neutralizing the filament with from 30% to 70% sodium hydroxide or potassium hydroxide solution, (v) washing the filament with water and (vi) drying the filament. The resulting filament was shortened as originally cut, and each end was 0.03 mm or less in diameter, appearing needle-like, as shown in FIG. 3. This form is described as "highly tapered".
The stiffness of PBT or PET-made highly tapered bristles produced by the technique of the cited patent was considerably decreased, and thereby, the bristles were made soft and did not damage the gums during brushing. Moreover, plaque in periodontal pockets could be removed by the highly tapered bristles during brushing. However, toothbrushes with highly tapered bristles exhibited the following disadvantages:
(1) Since the highly tapered bristles were prepared using chemical reagent, the tapering was too sensitive to operative conditions such as the concentration of the reagent used, the temperature, the duration of soaking, etc. and the ends of the highly tapered bristles were not uniform to a high frequency. That is, it was very difficult to obtain the highly tapered bristles with ends being uniform. As a result, an inferior product was produced in as many as half the attempts i.e, at least 50% of products were a loss. PA1 (2) The highly tapered bristles were felt too soft by consumers who were used to the proper flexibility of nylon-made bristles. The resulting feeling while brushing was evaluated lowly. PA1 (3) Although the highly tapered bristles could remove plaque in periodontal pockets better than the prior rounded or tapered bristles, their capability of removing plaque was evaluated substantially less than that expected. PA1 (4) Where the highly tapered bristles were more than 11.5 mm in length, they tended to be easily deformed during brushing.
Therefore, it is necessary to develop a PBT or PET-made highly tapered bristle that exhibits improved softness and durability, while more effectively removing plaque. At the same time, there is an urgent need to remarkably reduce the inferior goods rate, thereby lessening the cost of production.